Power electronics converter based reconfigurable grid emulation platform

ABSTRACT

A system includes a controller that is configured to generate a node control signal and a plurality of switch control signals, a plurality of programmable emulators, each of the plurality of programmable emulators being configurable as one of a plurality of node types responsive to the node control signal, and a plurality of switches that are programmable to couple ones of the plurality of programmable emulators to each other responsive to the plurality of switch control signals.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract numberNSF EEC-1041877 awarded by the National Science Foundation. Thegovernment has certain rights in the invention.

BACKGROUND

The present disclosure relates to power systems, and, in particular, toemulation of power systems.

Offline digital simulations have been used to predict the behavior ofelectrical systems in time domain due to their generally low cost, easyaccessibility, and flexible configuration. However, due to thelimitations of the computational resources and run time, the simulationaccuracy and fidelity may suffer from different levels of modelreductions. In some circumstances, the results depend on the solver andtime steps selected, and may have numerical stability and convergenceissues. Also, the simulation may be unreasonable time-consuming.Integrated circuit devices, such as microprocessors orField-Programmable Gate Arrays (FPGAs), have enabled real-time digitalsimulations. With deliberately designed network solutions and parallelcomputing techniques, these tools can simulate a relatively large systemin real-time with fixed time-steps. They can incorporate digital andanalog inputs and outputs to connect with the physical world to form aHardware in the Loop (HIL) simulation. This may allow the real-timetesting of developed system controllers without having to develop a realhardware test platform. Because the digital simulations still usemathematical models, the numerical stability of the digital simulationsmay be problematic. These non-real-time or real-time digital simulationtools may offer a large diversity of pre-defined models, and may havethe capability to integrate user built models. Nevertheless, manycritical conditions in the simulations tend to be simplified or ignoredby the users, such as measurement errors, control and communication timedelays, device physical bounds and saturation, electromagneticinterference. Accounting for the uncertainties in the simulations may becomputationally challenging, but failing to address these issues maycause unrealistic or incorrect results. Conversely, hardware-basedsystem testing can reveal the impact of the neglected aspects of digitalsimulations. A hardware-based validation may be required before thedeployment of any proposed controllers or developed devices. To assistwith such a testing or verification need, a real-time digital simulatorcan be paired with a power amplifier to form a Power HIL (PHIL) testplatform. The PHIL platform can be connected to an Equipment under Test(EUT) and may be used to evaluate its behavior with the remainder of thesystem represented by the simulator. While the PHIL platform may haveimproved fidelity to test the equipment, the overall system simulationaccuracy may not be better than that of a digital simulation. To studyoverall system behavior, researchers have built a down-scaled powertestbed, which has been modified over time to incorporate newtechnologies. Examples include the National Renewable EnergyLaboratory's (NREL) Energy Systems Integration Facility (ESIF) and theConsortium for Electric Reliability Technology Solutions' (CERTS)microgrid testing platform. While these down-scaled hardware-basedtesting platforms may provide superior fidelity, they are generallybulky and costly. Their topology and configurations are generallydifficult to change, usually requiring physical rewiring and componentreplacements for testing in a different system configuration or usingdifferent parameters. Another challenging simulation issue is resealing.To precisely represent a power component with different power andvoltage, the emulator should have the same per unit value of theoriginal one. This may be relatively easy for the passive componentslike resistors, inductors, and capacitors, but may be more difficult forrotating machines with different impedances, inertia, and saturationlevels. Transmission lines may also pose challenges as many cascadedcircuits made up of inductors and capacitors may be required torepresent the distributed parameters.

SUMMARY

In some embodiments of the inventive concept, a system comprises acontroller that is configured to generate a node control signal and aplurality of switch control signals, a plurality of programmableemulators, each of the plurality of programmable emulators beingconfigurable as one of a plurality of node types responsive to the nodecontrol signal, and a plurality of switches that are programmable tocouple ones of the plurality of programmable emulators to each otherresponsive to the plurality of switch control signals.

In other embodiments, the plurality of programmable emulators comprisesa first plurality of programmable emulators, the system furthercomprising a second plurality of programmable emulators, each of thesecond plurality of programmable emulators being configurable as along-distance transmission line emulator, a Direct Current (DC) lineemulator, a high voltage DC converter emulator, or a short-distancetransmission line emulator. The plurality of switches are furtherprogrammable to couple ones of the second plurality of programmableemulators to each other responsive to the plurality of switch controlsignals from the controller and to couple the ones of the firstplurality of programmable emulators to the ones of the second pluralityof programmable emulators to each other responsive to the plurality ofswitch control signals from the controller.

In still other embodiments, the long-distance transmission lineemulator, DC line emulator, and high voltage DC converter emulator eachcomprise a pair of power converters coupled together.

In still other embodiments, the controller is further configured togenerate a long distance transmission line control signal and thelong-distance transmission line emulator is configurable as a T modeltransmission line, a distributed model transmission line, or a FlexibleAlternating Current Transmission System (FACTS) model transmission lineresponsive to the long distance transmission line control signal.

In still other embodiments, the short-distance transmission lineemulator comprises at least one inductor.

In still other embodiments, the controller is further configured togenerate a short-distance transmission line signal, the short-distancetransmission line emulator comprises a plurality of inductors, and theplurality of switches are further programmable to couple ones of theplurality of inductors to each other to adjust a transmission linelength of the short-distance transmission line emulator responsive tothe short-distance transmission line signal.

In still other embodiments, the plurality of node types comprises aplurality of sources and a plurality of loads.

In still other embodiments, the plurality of sources comprises acoal-fired power generator, a gas power generator, a nuclear powergenerator, and a plurality of distributed energy resources.

In still other embodiments, the plurality of distributed energyresources comprises a wind power generator, a photovoltaic powergenerator, a biomass power generator, a biogas power generator, ageothermal power generator, a hydroelectric power generator, and anelectricity storage system.

In still other embodiments, the electricity storage system comprises abattery, an ultracapacitor, a flywheel, a compressed air storage device,and/or a responsive load.

In still other embodiments, the plurality of loads comprises a constantimpedance load, a constant current load, a constant power load, athree-phase induction motor load, a single-phase induction motor load,and/or a power electronic fed load.

In still other embodiments, the power electronic fed load comprises avariable speed drive, a data center power supply, a consumer electronicspower supply, and/or an electric vehicle charger.

In still other embodiments, each of the plurality of programmableemulators comprises a power converter.

In still other embodiments, the power converter comprises a three-phaseDirect Current/Alternating Current (DC/AC) converter.

In still other embodiments, the controller is further configured togenerate a mode control signal. Each of the plurality of programmableemulators is further configurable as one of a plurality of operatingmodes responsive to the mode control signal.

In still other embodiments, the plurality of operating modes comprisesMaximum Power Point Tracking (MPPT), power curtailment, droop control,inertia emulation, power factor control, voltage control, frequencycontrol, and/or reactive power support.

In still other embodiments, the system further comprises a Real TimeDigital Simulation (RTDS) system that is coupled to the plurality ofprogrammable emulators and is configured to digitally emulate a powersystem source, load, or fault.

In some embodiments of the inventive concept, a method comprisesgenerating, using a controller, a node control signal and a plurality ofswitch control signals, configuring each of a plurality of programmableemulators as one of a plurality of node types responsive to a nodecontrol signal from a controller responsive to the node control signal,and programming a plurality of switches to couple ones of theprogrammable emulators to each other responsive to the plurality ofswitch control signals.

In further embodiments, the plurality of programmable emulatorscomprises a first plurality of programmable emulators. The methodfurther comprises configuring each of a second plurality of programmableemulators as a long-distance transmission line emulator, a DirectCurrent (DC) line emulator, a high voltage DC converter emulator, or ashort-distance transmission line emulator, programming the plurality ofswitches to couple ones of the second plurality of programmableemulators to each other responsive to the plurality of switch controlsignals, and programming the plurality of switches to couple the ones ofthe first plurality of programmable emulators to the ones of the secondplurality of programmable emulators to each other responsive to theplurality of switch control signals.

In still further embodiments, the long-distance transmission lineemulator, DC line emulator, and high voltage DC converter emulator eachcomprise a pair of power converters coupled together.

In still further embodiments, the method further comprises generating,using the controller, a long distance transmission line control signaland configuring the long-distance transmission line emulator as a Tmodel transmission line, a distributed model transmission line, or aFlexible Alternating Current Transmission System (FACTS) modeltransmission line responsive to a long distance transmission linecontrol signal from the controller.

In still further embodiments, the short-distance transmission lineemulator comprises at least one inductor.

In still further embodiments, the short-distance transmission lineemulator comprises a plurality of inductors. The method furthercomprises generating, using the controller, a short-distancetransmission line signal and programming the plurality of switches tocouple ones of the plurality of inductors to each other to adjust atransmission line length of the short-distance transmission lineemulator responsive to the short-distance transmission line signal.

In still further embodiments, the method further comprises generating,using the controller, a mode control signal and configuring each of theplurality of programmable emulators as one of a plurality of operatingmodes responsive to the mode control signal.

In some embodiments of the inventive concept, a computer program productcomprises a tangible computer readable storage medium comprisingcomputer readable program code embodied in the medium that is executableby a processor to perform operations comprising: generating, using acontroller, a node control signal and a plurality of switch controlsignals, configuring each of a plurality of programmable emulators asone of a plurality of node types responsive to a node control signalfrom a controller responsive to the node control signal, and programminga plurality of switches to couple ones of the programmable emulators toeach other responsive to the plurality of switch control signals.

In other embodiments, the plurality of programmable emulators comprisesa first plurality of programmable emulators. The operations furthercomprise configuring each of a second plurality of programmableemulators being configurable as a long-distance transmission lineemulator, a Direct Current (DC) line emulator, a high voltage DCconverter emulator, or a short-distance transmission line emulator,programming the plurality of switches to couple ones of the secondplurality of programmable emulators to each other responsive to theplurality of switch control signals, and programming the plurality ofswitches to couple the ones of the first plurality of programmableemulators to the ones of the second plurality of programmable emulatorsto each other responsive to the plurality of switch control signals.

It is noted that aspects described with respect to one embodiment may beincorporated in different embodiments although not specificallydescribed relative thereto. That is, all embodiments and/or features ofany embodiments can be combined in any way and/or combination. Moreover,other methods, systems, articles of manufacture, and/or computer programproducts according to embodiments of the inventive subject matter willbe or become apparent to one with skill in the art upon review of thefollowing drawings and detailed description. It is intended that allsuch additional systems, methods, articles of manufacture, and/orcomputer program products be included within this description, be withinthe scope of the present inventive subject matter, and be protected bythe accompanying claims. It is further intended that all embodimentsdisclosed herein can be implemented separately or combined in any wayand/or combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of embodiments will be more readily understood from thefollowing detailed description of specific embodiments thereof when readin conjunction with the accompanying drawings, in which:

FIGS. 1A, 1B, and 1C are block diagrams that illustrates a networkenvironment for a power electronics converter based reconfigurable gridemulation platform in accordance with some embodiments of the inventiveconcept;

FIG. 2 is a schematic of a programmable emulator of FIG. 1A for use as apower source or load according to some embodiments of the inventiveconcept;

FIG. 3 is a schematic of a hybrid power electronics converter basedreconfigurable grid emulation platform including a Real Time DigitalSimulation (RTDS) system;

FIG. 4 is a schematic of a programmable emulator of FIG. 1C for use as along-distance transmission line and/or a DC line or high voltage DCconverter according to some embodiments of the inventive concept;

FIG. 5 is a schematic of a programmable emulator of FIG. 1B for use as ashort-distance transmission line according to some embodiments of theinventive concept;

FIG. 6 is a block diagram that illustrates a programming of aprogrammable emulator as a photovoltaic power generator according tosome embodiments of the inventive concept;

FIG. 7 is a block diagram that illustrates a programming of aprogrammable emulator as a long-distance T model transmission lineaccording to some embodiments of the inventive concept;

FIG. 8 is a block diagram that illustrates a programming of aprogrammable emulator as a short-distance transmission line according tosome embodiments of the inventive concept;

FIG. 9 is a block diagram that illustrates a programming of an operationmode of a programmable emulator configured as a power generatoraccording to some embodiments of the inventive concept;

FIGS. 10 and 11 are flowcharts that illustrate operations of a powerelectronics converter based reconfigurable grid emulation platformaccording to some embodiments of the inventive concept;

FIG. 12 is a diagram of a two-area power generation grid for emulationaccording to some embodiments of the inventive concept;

FIGS. 13A and 13B illustrate programmable emulators of the powerelectronics converter based reconfigurable grid emulation platform ofFIG. 1 for use in emulating the two-area power generation grid of FIG.12 according to some embodiments of the inventive concept;

FIGS. 14A and 14B illustrate an interconnection of the programmableemulators of FIGS. 13A and 13B for emulating the two-area powergeneration grid of FIG. 12 according to some embodiments of theinventive concept;

FIG. 15 is a simplified block diagram of the controller used in thepower electronics converter based reconfigurable grid emulation platformof FIGS. 1A, 1B, 1C according to some embodiments of the inventiveconcept; and

FIG. 16 is a simplified block diagram of a programmable emulator used inthe power electronics converter based reconfigurable grid emulationplatform of FIGS. 1A, 1B, 1C according to some embodiments of theinventive concept.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth to provide a thorough understanding of embodiments of the presentdisclosure. However, it will be understood by those skilled in the artthat the present invention may be practiced without these specificdetails. In some instances, well-known methods, procedures, componentsand circuits have not been described in detail so as not to obscure thepresent disclosure. It is intended that all embodiments disclosed hereincan be implemented separately or combined in any way and/or combination.Aspects described with respect to one embodiment may be incorporated indifferent embodiments although not specifically described relativethereto. That is, all embodiments and/or features of any embodiments canbe combined in any way and/or combination.

As used herein, the term a data processing system may include, but it isnot limited to, a hardware element, firmware component, and/or softwarecomponent.

As used herein, the term “load” refers to any system, device, apparatus,or the like that consumes power.

As used herein a microgrid is an energy or power distribution networkthat may include one or more distributed energy resources and loads thatare capable of operating in concert with or independently of a mainpower grid.

As used herein a distributed energy resource (DER) is a decentralizedpower generation source that typically outputs less power than thecentralized power stations used in the main power grid to distributepower over large distances, such as coal-fired, gas, and nuclear poweredplants. A DER system typically has a capacity of 10 MW or less and islocated relatively close to the loads that it serves. A DER system maybe part of a microgrid and may be used to provide power to the microgridloads when the microgrid is connected to the main power grid and also attimes when the microgrid is disconnected from the main power grid andoperating in islanded mode. DER systems typically use diesel generatorsets, natural gas microturbines, fuel cells, or renewable energyresources to generate power including, but not limited to, wind,photovoltaic (solar), biomass, biogas, geothermal, and/or hydroelectric.An electricity storage system (ESS), which can be used to store excesspower that is generated during times of low demand, for example, mayalso be classified as a DER system. The electricity storage system maycomprise a battery, an ultracapacitor, a flywheel, a compressed airstorage device and/or a responsive load.

Some embodiments of the inventive concept stem from a realization that anetwork of programmable emulators based on power converters andconnected by switches under the operational supervision of a controllermay provide a flexible emulation platform for electrical systems, suchas power grids. The power converter based reconfigurable grid emulationplatform may provide a more realistic simulation without the numericalstability and convergence issues associated with computer software basedsimulation systems while providing more flexibility and model fidelitythan a scaled hardware based testing platform. The power converter basedreconfigurable grid emulation platform, according to some embodiments ofthe inventive concept, may further provide efficient automatedreconfiguration when reconfiguring the power converters to emulatedifferent types of elements, systems, operational modes, and/or controlparameters as well as reconfiguring an entire system network to adifferent topology. This may reduce idle time when transforming anemulation platform from one test environment to another testenvironment.

Referring to FIGS. 1A, 1B, and 1C a network environment for a powerelectronics converter based reconfigurable grid emulation platform,according to some embodiments of the inventive concept, comprises acentral controller 105 and a plurality of cabinets 110 a, 110 b, and 110c, Type I, Type II, and Type III, which are coupled by a bus 115. TheType I cabinet 110 a comprises a plurality of Clusters 1 through n witheach cluster comprising one or more programmable emulators. In theexample shown in FIGS. 1A, 1B, 1C, Cluster 1 includes three emulators(Emulators 111, 112, and 113), which are connected to a power supply byway of a DC bus and a rectifier as shown. Inductors Lp1, Lp2, Lp3 andcapacitor C4 may provide filtering functionality in the connection ofthe Emulators 111, 112, and 113 to the power supply. Emulator 1 iscoupled to a set of inductors L11, L12, and L13 and a capacitor C1,Emulator 2 is coupled to a set of inductors L21, L22, and L23 and acapacitor C2, and Emulator 3 is coupled to a set of inductors L31, L32,and L33 and a capacitor C3. Thus, each of the clusters Cluster 2 throughCluster n may be configured with a rectifier and one or more filteringinductors and capacitors to support the emulators associated therewith.Each of the emulators in the Type I cabinet may be used to emulate anode representing one or more sources, e.g., power generation sources,or loads. The loads may include, but are not limited to, a constantimpedance load, a constant current load, a constant power load, athree-phase induction motor load, a single-phase induction motor load,and/or a power electronic fed load. The power electronic fed load mayinclude, but is not limited to, a variable speed drive, a data centerpower supply, a consumer electronics power supply, and/or an electricvehicle charger. The Type II cabinet 110 b comprises a plurality ofClusters n+1 through m with each cluster comprising one or more variablelength inductors 120, 122. Each of these variable length inductors maybe used to emulate a short-distance transmission line. The Type IIIcabinet 110 comprises a plurality of Clusters m+1 through s with eachcluster comprising one or more pairs of emulators coupled back to back.As shown in FIG. 1C, Cluster m+1 includes emulators 131 and 132 coupledback to back with a filtering capacitor C5 therebetween and emulators133 and 134 coupled back to back with a filtering capacitor C6therebetween. Emulator 131 is coupled to a set of inductors L41, L42,and L43, Emulator 132 is coupled to a set of inductors L51, L52, andL53, and Emulator 133 is coupled to a set of inductors L61, L62, andL63, and Emulator 134 is coupled to a set of inductors L71, L72, andL73. The pair of back-to-back emulators 131 and 132 in the Type IIIcabinet may be used to emulate a long-distance transmission line. Thepair of back-to-back emulators 133 and 134 may be used to emulate DClines and/or high voltage DC converters. The Type I cabinet 110 a, TypeII cabinet 110 b, and Type III cabinet 110 c may comprise a plurality ofswitches S1, S2, S3, S(k+1), S(k+2), S(k+3), S(k+4), S(p+1), S(p+2),S(p+3), S(p+4), which may allow the various emulated nodes of the Type Icabinet 110 a, the short-distance transmission lines of the Type IIcabinet 110 b, and the long-distance transmission lines of the Type IIIcabinet 110 c to be coupled to one another.

The central controller 105 may comprise a data processing systemincluding a processor and a memory coupled thereto. The processorcommunicates with the memory via an address/data bus. The processor maybe, for example, a commercially available or custom microprocessor. Thememory is representative of the one or more memory devices containingthe software and data used for managing a power electronic converterbased reconfigurable grid emulation platform in accordance with someembodiments of the inventive concept. The memory may include, but is notlimited to, the following types of devices: cache, ROM, PROM, EPROM,EEPROM, flash, SRAM, and DRAM. As shown in FIGS. 1A, 1B, and 1C, thecentral controller 105 may comprise an emulator reconfiguration module150, an emulator parameters reconfiguration module 160, an emulatorcontrol modes reconfiguration module 170, and a system topologyreconfiguration module 180. As will be described herein, the emulatorreconfiguration module 150 and the emulator parameters reconfigurationmodule 160 may be configured to control the configuration of the variousemulated nodes of the Type I cabinet 110 a, the short-distancetransmission lines of the Type II cabinet 110 b, and the long-distancetransmission lines of the Type III cabinet 110 c. The emulator controlmodes reconfiguration module 170 may be configured to control anoperational mode configuration of the various emulated nodes of the TypeI cabinet 110 a. The system topology reconfiguration module 180 may beconfigured to control the programming states of the plurality ofswitches S1, S2, S3, S(k+1), S(k+2), S(k+3), S(k+4), S(p+1), S(p+2),S(p+3), S(p+4) in the Type I cabinet 110 a, Type II cabinet 110 b, andType III cabinet 110 c to connect the various emulated nodes, emulatedshort-distance transmission lines, and emulated long-distancetransmission lines in a desired topology to emulate, for example, apower grid, micro-grid, or combined power grid and micro-grid.

Although FIGS. 1A, 1B, 1C illustrate hardware/software architecturesthat may be used in data processing systems, such as the centralcontroller 105 of FIGS. 1A, 1B, 1C, for managing a power electronicconverter based reconfigurable grid emulation platform in accordancewith some embodiments of the inventive concept, it will be understoodthat the present invention is not limited to such a configuration but isintended to encompass any configuration capable of carrying outoperations described herein. Computer program code for carrying outoperations of data processing systems described herein may be written ina high-level programming language, such as Python, Java, C, and/or C++,for development convenience. In addition, computer program code forcarrying out operations of embodiments of the present invention may alsobe written in other programming languages, such as, but not limited to,interpreted languages. Some modules or routines may be written inassembly language or even micro-code to enhance performance and/ormemory usage. It will be further appreciated that the functionality ofany or all of the program modules may also be implemented using discretehardware components, one or more application specific integratedcircuits (ASICs), or a programmed digital signal processor ormicrocontroller.

Moreover, the functionality of the central controller 105 of FIG. 1 maybe implemented as a single processor system, a multi-processor system, amulti-core processor system, or even a network of stand-alone computersystems, in accordance with various embodiments of the inventive subjectmatter. Each of these processor/computer systems may be referred to as a“processor” or “data processing system.” It will be further understoodthat the functionality provided by various modules of the centralcontroller 105 may, in other embodiments, be performed in whole or inpart on other processors, such as in the various emulators of the Type Icabinet 110 a, Type II cabinet 110 b, and Type III cabinet 110 c.

The central controller 105 of FIG. 1A may be used to facilitate themanagement of a power electronic converter based reconfigurable gridemulation platform, according to various embodiments described herein.These apparatus may be embodied as one or more enterprise, application,personal, pervasive and/or embedded computer systems and/or apparatusthat are operable to receive, transmit, process and store data using anysuitable combination of software, firmware and/or hardware and that maybe standalone or interconnected by any public and/or private, realand/or virtual, wired and/or wireless network including all or a portionof the global communication network known as the Internet, and mayinclude various types of tangible, non-transitory computer readablemedia.

FIG. 2 is a schematic of a programmable emulator, such as theprogrammable emulators 111, 112, and 113 of FIG. 1A, for use as a powersource or load in an emulation platform according to some embodiments ofthe inventive concept. The programmable emulator 200 comprises a powerconverter 205, filter inductors 210, and filter capacitor 215 that areconnected as shown. A load or source may be emulated based on itsvoltage and current characteristics. For example, the input current andvoltage to the power converter 205 may be measured and the powerconverter 205 may then be configured to generate an output current orvoltage that is proportional to a source or load being emulated. Thecomponents in an electrical system may be considered as either voltagesource components or current source components. The power converter 205may have two types of control schemes: a first type regulates theterminal voltage and a second type regulates the output current. In someembodiments, the power converter 205 may measure the emulated inputvoltage and/or current and generate a desired emulated output currentwhen emulating a load. In other embodiments, the power converter 205 maymeasure the emulated input voltage and/or current and generated adesired emulated output voltage when emulating a source, e.g., a powergenerator. The power converter may be a three-phase DC/AC converter insome embodiments of the inventive concept

FIG. 3 is a schematic of a hybrid power electronics converter basedreconfigurable grid emulation platform including a Real Time DigitalSimulation (RTDS) system. The hybrid system includes an RTDS digitalpower system simulator 300 that may simulate one or more powergeneration sources G1-Gn and one or more loads LD1-LDn. The RTDS powersystem simulator 300 may communicate with a power electronics converterbased reconfigurable grid emulation platform 305 including emulators 1-nas described above with respect to the emulators of cabinets 110 a, 110b, and 110 c via a signal change and a power interface module. Theemulators 1-n are supported by a DC power supply and communicate witheach other and the RTDS power system simulator 300 via an AC link. Thus,a power system may be emulated using both physical power electronicsconverters as well a digital simulation system to provide additionalflexibility the size, scope, and types of power sources, loads, faults,and the like being emulated.

FIG. 4 is a schematic of a programmable emulator, such as theprogrammable emulators 131, 132, 133, and 134 of FIG. 1, for use as along-distance transmission line, a DC line, and/or a high voltage DCconverter in an emulation platform according to some embodiments of theinventive concept. The programmable emulator 400 comprises a powerconverter 405 a and filter inductors 410 a that are coupled to a powerconverter 405 b and filter inductors 410 b along with a filter capacitor415 therebetween. The programmable emulator 400 that may be used toemulate a long-distance transmission line, a DC line, and/or a highvoltage DC converter may comprise two power emulators 200 of FIG. 2 usedto emulate a load or source coupled back-to-back.

FIG. 5 is a schematic of a programmable emulator, such as theprogrammable emulators 120 and 122 of FIG. 1B, for use as ashort-distance transmission line in an emulation platform according tosome embodiments of the inventive concept. The programmable emulator 500comprises a plurality of inductors that may be coupled in variousconfigurations using one or more of the switches S(k+1), S(k+2), S(k+3),S(k+4) of FIG. 1B so as to have a desired length.

FIG. 6 is a block diagram that illustrates a programming of aprogrammable emulator, such as the programmable emulators 111, 112, and113 of FIG. 1A, for use as a photovoltaic power generator in anemulation platform according to some embodiments of the inventiveconcept. The emulator reconfiguration module 150 along with the emulatorparameters reconfiguration module 160 of FIG. 1A may include a librarythat can be used to program the emulators in the Type I cabinet 110 a toserve as a particular node type in an electrical system, such as anelectrical power grid. Thus, the emulator reconfiguration module 150along with the emulator parameters reconfiguration module 160 mayincorporate access to a model selection module 605 to select among alibrary 610 of various source and load types that can be used forconfiguring the Type I cabinet 110 a emulators. As shown in FIG. 6, asolar or photovoltaic energy model 615, a general generator (i.e.,source) model 620, and a general load model 625 are shown as optionswith the solar energy model 615 being selected. It will be understood,however, that the various node types are not limited to these particularmodels. For example, in some embodiments, the source node types mayinclude, but are not limited to, a coal-fired power generator, a gaspower generator, a nuclear power generator, and a Distributed EnergyResource (DER). Moreover, in further embodiments, the DER types mayinclude, but are not limited to, a wind power generator, a photovoltaicpower generator, a biomass power generator, a biogas power generator, ageothermal power generator, a hydroelectric power generator, and anelectricity storage system. In the example of FIG. 5, the solar(photovoltaic) power energy model is loaded by way of a node controlsignal generated by the central controller 105 into an emulator 200 ofthe type described above with respect to FIG. 2 to configure theemulator as a solar energy source. To emulate a solar power energysource, the emulator 200 may be configured to emulate a Boostconfiguration including a Boost converter 650, an inverter 655, a filter660, and an emulated photovoltaic panel 665. Although a Boostconfiguration is illustrated for emulating a photovoltaic energy source,it will be understood that other power converter embodiments may beemulated as part of an emulation of other types of sources, loads, shortcircuits or faults in accordance with various embodiments of theinventive concept. In addition to the particular model for the emulator200, the emulator parameters reconfiguration module 160 may download oneor more parameters, data, or other information that may be used toconfigure and control operation of the programmable emulator 200. Theseparameters may be used to control the output voltage and/or currentlevels to tune the programmable emulator 200 to better simulate adesired energy source, load, and/or short circuit.

FIG. 7 is a block diagram that illustrates a programming of aprogrammable emulator, such as the programmable emulators 131 and 132 ofFIG. 1C, for use as a long-distance transmission line in an emulationplatform according to some embodiments of the inventive concept. Theprogrammable emulators 133 and 134 may be programmed in a similar mannerto emulate a DC line and/or a high voltage DC converter responsive to aDC line or DC high voltage converter control signal from the centralcontroller 105. Similar to the node configuration illustrated in FIG. 6,the emulator reconfiguration module 150 along with the emulatorparameters reconfiguration module 160 of FIG. 1C may include a librarythat can be used to program the emulators in the Type III cabinet 110 cto serve as a long-distance transmission line in an electrical system,such as an electrical power grid. Thus, the emulator reconfigurationmodule 150 along with the emulator parameters reconfiguration module 160may incorporate access to a model selection module 705 to select among alibrary 710 of various long-distance transmission line types that can beused for configuring the Type III cabinet 110 c emulators. As shown inFIG. 7, a distributed model 715, a T model 720, and a FlexibleAlternating Current Transmission Systems (FACTS) model are shown withthe T model 720 being selected. It will be understood, however, that thevarious types of long-distance transmission lines are not limited tothese particular models. Other types of long-distance transmission linemodels may be used in accordance with other embodiments of the inventiveconcept. In the example of FIG. 7, the T model long-distancetransmission line model is loaded by way of a long-distance transmissionline control signal into an emulator 400 of the type described abovewith respect to FIG. 4 to operate the emulator power converter pairsincluded therein as a T model long-distance transmission line. The powerconverters 405 a and 405 b are configured so that in conjunction withthe filter inductors 410 a and 410 b the emulated long-distancetransmission line has an equivalent circuit corresponding to theinductors R7, L7, and C7 configured as shown in FIG. 7.

FIG. 8 is a block diagram that illustrates a programming of aprogrammable emulator, such as the programmable emulators 120 and 122 ofFIG. 1B, for use as a short-distance transmission line in an emulationplatform according to some embodiments of the inventive concept. Similarto the node configuration illustrated in FIG. 6 and the long-distancetransmission line configuration illustrated in FIG. 7, the emulatorreconfiguration module 150 along with the emulator parametersreconfiguration module 160 of FIG. 1 may include a line distanceselection module 805 that is configured to program the length of theinductors included in the programmable emulator 500, which may be usedto implement the programmable emulators 120 and 122 in the Type IIcabinet of FIG. 1B. In the example of FIG. 8, the switches S(k+1),S(k+2), S(k+3), S(k+4) of FIG. 1B are configured in an open or closedstate based on a short-distance transmission line signal generated bythe central controller 105 to adjust the inductive length of theinductors of the programmable emulator 500 to generate a programmedemulator 810 that emulates a short-distance transmission line with aninductive length of L8.

FIG. 9 is a block diagram that illustrates a further programming of aprogrammable emulator, such as the programmable emulators 111, 112, and113 of FIG. 1A to specify an operating mode of a node for emulation inan emulation platform according to some embodiments of the inventiveconcept. The library 610 of FIG. 6 may further include an operationalmode selection capability for the various node types. In the exampleshown in FIGS. 6 and 9, a control mode selection model 905 may be usedto select among a library 610 of various operational mode types that canbe used for configuring Type I cabinet 110 a emulators. As shown in FIG.9, the operating modes may include, but are not limited to, a MaximumPower Point Tracking (MPPT) mode 910, a power curtailment mode 915, anda reactive power support mode 920. Other operations modes may include,but are not limited to, a power curtailment mode, a droop control mode,an inertia emulation mode, a power factor control mode, a voltagecontrol mode, and a frequency control mode. Although illustrated withrespect to a node being configured as a solar or photovoltaic generator,it will be understood that the operating modes are applicable to othertypes of generator, energy storage, or load types in accordance withvarious embodiments of the inventive concept. In the example of FIG. 9,the MPPT operating mode 910 model is loaded by way of a mode controlsignal generated by the central controller 105 into an emulator 200 ofthe type described above with respect to FIG. 2 to operate the emulatoras a solar energy source with an MPPT operating mode.

FIGS. 10 and 11 are flowcharts that illustrate operations of a powerelectronics converter based reconfigurable grid emulation platformaccording to some embodiments of the inventive concept. Referring toFIG. 10, operations begin at block 1000 where the central controller 105generates one or more node control signals for configuring one or moreemulators in the Type I cabinet 110 a, i.e., a first plurality ofemulators, as particular node types, such as sources (e.g., powergenerators), loads, energy storage, and/or short circuits. At block1010, the power converters in the one or more emulators in the Type Icabinet are configured in accordance with the one or more node typesspecified by the central controller 105. The central controller 105generates switch control signals to program the switches in the gridemulation platform to couple ones of the programmable emulators togetherat block 1020. Referring now to FIG. 11, operations begin at block 1100where the one or more emulators in the Type III and Type II cabinets 110c and 110 b, respectively, are operated as long-distance transmissionline emulators, DC lines, high voltage DC converters and/orshort-distance transmission line emulators, i.e., second plurality ofemulators, responsive to one or more long-distance transmission linecontrol signals, DC line control signals, DC converter control signalsand/or short-distance transmission line control signals, respectively,generated by the central controller 105. The central controller 105generates switch control signals to program the switches in the gridemulation platform to couple ones of the second plurality ofprogrammable emulators together at block 1110 and generates switchcontrol signals to program the switches in the grid emulation platformto couple ones of the first plurality of programmable emulators to onesof the second plurality of programmable emulators at block 1120.

Embodiments of the inventive concept may be illustrated by way ofexample. Referring to FIG. 12, a two-area power generation grid foremulation includes four power generators G1, G2, G3, and G4 and twoloads L7 and L9 that are connected by various buses, switches, andtransmission lines 1-11 and X1-X4, which may be transformers emulated intransmission lines. Referring to FIG. 13, the central controller 105 mayselect source and load emulators from the Type I Cabinet 110 a toemulate the power generators G1-G4 and loads L7 and L9 of FIGS. 1A, 1B,1C, may select short-distance transmission line emulators from the TypeII cabinet 110 b to emulate short-distance transmission lines to connectelements of the emulated two-area power generation grid of FIG. 12together, and may select long-distance transmission line emulators fromthe Type III cabinet 110 c to connect elements of the emulated two-areapower generation grid of FIG. 12 together. In the example shown in FIGS.13A and 13B, six emulators (Emulators 1-6) across Clusters 1 and 2 areselected from the Type I cabinet, six emulators (Emulators 7-12) fromCluster 3 are selected from the Type II cabinet, and three emulators(Emulators 13-15) from Cluster 4 are selected from the Type III cabinet.As will be described below, the various emulators may be allocated inclusters based on connections to system power and other supportinginfrastructure, but not all emulators in a cluster may be used in aparticular emulation. The central controller 105 may selectively programswitches S1-S24 to connect the various emulators 1-16 together to matchthe topological configuration of the two-area power generation grid ofFIG. 12. Referring to FIGS. 14A and 14B, the central controller 105programs switches S1, S2, S3, and S7-S12 to connect Emulators 1-3 asgenerators G1, G2, and load L7, respectively, to emulate Area 1 of FIG.12. Emulators 7-9 are connected between Emulators 1-3 to emulateshort-distance transmission lines in Area 1. Similarly, the centralcontroller 105 programs switches S4-S6 and S13-S18 to connect Emulators4-6 as generators G3, G4, and load L9, respectively, to emulate Area 2of FIG. 12. Emulators 10-12 are connected between Emulators 4-6 toemulate short-distance transmission lines in Area 2. The controllerprograms switches S19 and S20 to couple the Area 1 emulated elements tothe Area 2 emulated elements using Emulator 13 to emulate along-distance transmission line. In addition, the central controller 105may use control signals to communicate with each of the emulators(Emulators 1-13) to configure the emulators emulate the voltage and/orcurrent characteristics associated with the various generators, loads,transmission lines, etc. of the two-area power generation grid of FIG.12. Thus, some embodiments of the inventive concept may provide aflexible power electronics converter based grid emulation platform thatmay use modular emulators that may be programmed to emulate componentsof an electrical system, including source (generator), load, shortcircuit, and connectivity components. Moreover, these emulators may beconnected to and disconnected from each other using a network ofprogrammable switches, which may allow emulation of numerous types ofelectrical system topologies through use of a controller without theneed to manually configure the emulators.

FIG. 15 is a simplified block diagram of the central controller 105 usedin the power electronics converter based reconfigurable grid emulationplatform of FIGS. 1A, 1B, 1C that is configured to perform operationsaccording to one or more embodiments disclosed herein according to someembodiments of the inventive concept. The controller 1500 comprises aprocessor circuit 1502, a memory circuit 1510, and an interface 1520.The interface 1520 comprises a wireless transceiver 1530 and a networkadapter 1540. The wireless transceiver 1530 and the network adapter 1540may be configured to provide the controller 1500 with wireless andwireline communication functionality, respectively. In some embodiments,the interface 1520 may support a Joint Test Action Group (JTAG) port forcommunication. The processor circuit 1502 may comprise one or more dataprocessing circuits, such as a general purpose and/or special purposeprocessor, e.g., microprocessor and/or digital signal processor. Theprocessor circuit 1502 is configured to execute computer readableprogram code 1512 and emulation download modules 1514 (e.g., signals,data, and other information to configure programmable emulators withparticular voltage, current, short-circuit, and/or operating modecharacteristics) in the memory circuit 1510 to perform at least some ofthe operations described herein as being performed by the centralcontroller 105.

FIG. 16 is a simplified block diagram of a programmable emulator used inthe power electronics converter based reconfigurable grid emulationplatform of FIGS. 1A, 1B, 1C that is configured to perform operationsaccording to one or more embodiments disclosed herein according to someembodiments of the inventive concept. The emulator 1600 comprises aprocessor circuit 1602, a memory circuit 1610, and a network interface1620, which may receive DC power through the power circuit 1650. Thenetwork interface 1620 comprises a wireless transceiver 1630 and anetwork adapter 1640. The wireless transceiver 1630 and the networkadapter 1640 may be configured to provide the emulator 1600 withwireless and wireline communication functionality, respectively. Theprocessor circuit 1602 may comprise one or more data processingcircuits, such as a general purpose and/or special purpose processor,e.g., microprocessor and/or digital signal processor. The processorcircuit 1602 is configured to execute computer readable program code1612 and emulation configuration/mode modules 1614 (e.g., signals, data,and other information received from the central controller 105 toconfigure programmable emulators with particular voltage, current,short-circuit, and/or operating mode characteristics) in the memorycircuit 1610 to perform at least some of the operations described hereinas being performed by an emulator.

Some embodiments of the inventive concept may provide a powerelectronics converter based reconfigurable grid emulation platform that,when compared with purely digital or software simulations, providesbetter test stability and doesn't have similar numerical stability andconvergence issues attendant to such simulations. When compared withpurely hardware based emulation platforms, the power electronicsconverter based reconfigurable grid emulation platform may providegreater flexibility, improved cost efficiency, and a smallerimplementation size. Moreover, the platform may emulate short circuitfaults at buses or lines, including single-phase to ground, doubleline-to-ground, line-to-line, and three-phase faults. Embodiments of theinventive concept may also provide protective functions, such as, butnot limited to, undervoltage, overcurrent, overfrequency, andunderfrequency.

Further Definitions and Embodiments

In the above-description of various embodiments of the presentdisclosure, aspects of the present disclosure may be illustrated anddescribed herein in any of a number of patentable classes or contextsincluding any new and useful process, machine, manufacture, orcomposition of matter, or any new and useful improvement thereof.Accordingly, aspects of the present disclosure may be implementedentirely hardware, entirely software (including firmware, residentsoftware, micro-code, etc.) or combining software and hardwareimplementation that may all generally be referred to herein as a“circuit,” “module,” “component,” or “system.” Furthermore, aspects ofthe present disclosure may take the form of a computer program productcomprising one or more computer readable media having computer readableprogram code embodied thereon.

Any combination of one or more computer readable media may be used. Thecomputer readable media may be a computer readable signal medium or acomputer readable storage medium. A computer readable storage medium maybe, for example, but not limited to, an electronic, magnetic, optical,electromagnetic, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing. More specific examples (anon-exhaustive list) of the computer readable storage medium wouldinclude the following: a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an appropriateoptical fiber with a repeater, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium, may be any tangible medium that cancontain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device. Program codeembodied on a computer readable signal medium may be transmitted usingany appropriate medium, including but not limited to wireless, wireline,optical fiber cable, RF, etc., or any suitable combination of theforegoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C #, VB.NET,Python or the like, conventional procedural programming languages, suchas the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL2002, PHP, ABAP, LabVIEW, dynamic programming languages, such as Python,Ruby and Groovy, or other programming languages. The program code mayexecute entirely on the user's computer, partly on the user's computer,as a stand-alone software package, partly on the user's computer andpartly on a remote computer or entirely on the remote computer orserver. In the latter scenario, the remote computer may be connected tothe user's computer through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection may bemade to an external computer (for example, through the Internet using anInternet Service Provider) or in a cloud computing environment oroffered as a service such as a Software as a Service (SaaS).

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable instruction executionapparatus, create a mechanism for implementing the functions/actsspecified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that when executed can direct a computer, otherprogrammable data processing apparatus, or other devices to function ina particular manner, such that the instructions when stored in thecomputer readable medium produce an article of manufacture includinginstructions which when executed, cause a computer to implement thefunction/act specified in the flowchart and/or block diagram block orblocks. The computer program instructions may also be loaded onto acomputer, other programmable instruction execution apparatus, or otherdevices to cause a series of operational steps to be performed on thecomputer, other programmable apparatuses or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousaspects of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting of the disclosure. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Like reference numbers signify like elements throughoutthe description of the figures.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. Thus, a first element could be termed a secondelement without departing from the teachings of the inventive subjectmatter.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis specification and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

The present disclosure of embodiments has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many variations andmodifications can be made to the embodiments without substantiallydeparting from the principles of the present invention. All suchvariations and modifications are intended to be included herein withinthe scope of the present invention.

What is claimed is:
 1. A system, comprising: a controller that isconfigured to generate a node control signal and a plurality of switchcontrol signals; a plurality of programmable emulators, each of theplurality of programmable emulators being configurable as one of aplurality of node types responsive to the node control signal; and aplurality of switches that are programmable to couple ones of theplurality of programmable emulators to each other responsive to theplurality of switch control signals.
 2. The system of claim 1, whereinthe plurality of programmable emulators comprises a first plurality ofprogrammable emulators, the system further comprising: a secondplurality of programmable emulators, each of the second plurality ofprogrammable emulators being configurable as a long-distancetransmission line emulator, a Direct Current (DC) line emulator, a highvoltage DC converter emulator, or a short-distance transmission lineemulator; wherein the plurality of switches are further programmable tocouple ones of the second plurality of programmable emulators to eachother responsive to the plurality of switch control signals from thecontroller and to couple the ones of the first plurality of programmableemulators to the ones of the second plurality of programmable emulatorsto each other responsive to the plurality of switch control signals fromthe controller.
 3. The system of claim 2, wherein the long-distancetransmission line emulator, DC line emulator, and high voltage DCconverter emulator each comprise a pair of power converters coupledtogether.
 4. The system of claim 3, wherein the controller is furtherconfigured to generate a long distance transmission line control signal;and wherein the long-distance transmission line emulator is configurableas a T model transmission line, a distributed model transmission line,or a Flexible Alternating Current Transmission System (FACTS) modeltransmission line responsive to the long distance transmission linecontrol signal.
 5. The system of claim 2, wherein the short-distancetransmission line emulator comprises at least one inductor.
 6. Thesystem of claim 5, wherein the controller is further configured togenerate a short-distance transmission line signal; wherein theshort-distance transmission line emulator comprises a plurality ofinductors; and wherein the plurality of switches are furtherprogrammable to couple ones of the plurality of inductors to each otherto adjust a transmission line length of the short-distance transmissionline emulator responsive to the short-distance transmission line signal.7. The system of claim 1, wherein the plurality of node types comprisesa plurality of sources and a plurality of loads.
 8. The system of claim7, wherein the plurality of sources comprises a coal-fired powergenerator, a gas power generator, a nuclear power generator, and aplurality of distributed energy resources.
 9. The system of claim 8,wherein the plurality of distributed energy resources comprises a windpower generator, a photovoltaic power generator, a biomass powergenerator, a biogas power generator, a geothermal power generator, ahydroelectric power generator, and an electricity storage system. 10.The system of claim 9, wherein the electricity storage system comprisesa battery, an ultracapacitor, a flywheel, a compressed air storagedevice, and/or a responsive load.
 11. The system of claim 7, wherein theplurality of loads comprises a constant impedance load, a constantcurrent load, a constant power load, a three-phase induction motor load,a single-phase induction motor load, and/or a power electronic fed load.12. The system of claim 11, wherein the power electronic fed loadcomprises a variable speed drive, a data center power supply, a consumerelectronics power supply, and/or an electric vehicle charger.
 13. Thesystem of claim 1, wherein each of the plurality of programmableemulators comprises a power converter.
 14. The system of claim 13,wherein the power converter comprises a three-phase DirectCurrent/Alternating Current (DC/AC) converter.
 15. The system of claim1, wherein the controller is further configured to generate a modecontrol signal; wherein each of the plurality of programmable emulatorsis further configurable as one of a plurality of operating modesresponsive to the mode control signal.
 16. The system of claim 15,wherein the plurality of operating modes comprises Maximum Power PointTracking (MPPT), power curtailment, droop control, inertia emulation,power factor control, voltage control, frequency control, and/orreactive power support.
 17. The system of claim 1, further comprising: aReal Time Digital Simulation (RTDS) system that is coupled to theplurality of programmable emulators and is configured to digitallyemulate a power system source, load, or fault.
 18. A method, comprising:generating, using a controller, a node control signal and a plurality ofswitch control signals; configuring each of a plurality of programmableemulators as one of a plurality of node types responsive to a nodecontrol signal from a controller responsive to the node control signal;and programming a plurality of switches to couple ones of theprogrammable emulators to each other responsive to the plurality ofswitch control signals.
 19. The method of claim 18, wherein theplurality of programmable emulators comprises a first plurality ofprogrammable emulators, the method further comprising: configuring eachof a second plurality of programmable emulators as a long-distancetransmission line emulator, a Direct Current (DC) line emulator, a highvoltage DC converter emulator, or a short-distance transmission lineemulator; programming the plurality of switches to couple ones of thesecond plurality of programmable emulators to each other responsive tothe plurality of switch control signals; and programming the pluralityof switches to couple the ones of the first plurality of programmableemulators to the ones of the second plurality of programmable emulatorsto each other responsive to the plurality of switch control signals. 20.The method of claim 19, wherein the long-distance transmission lineemulator, DC line emulator, and high voltage DC converter emulator eachcomprise a pair of power converters coupled together.
 21. The method ofclaim 19, further comprising: generating, using the controller, along-distance transmission line control signal; and configuring thelong-distance transmission line emulator as a T model transmission line,a distributed model transmission line, or a Flexible Alternating CurrentTransmission System (FACTS) model transmission line responsive to along-distance transmission line control signal from the controller. 22.The method of claim 19, wherein the short-distance transmission lineemulator comprises at least one inductor.
 23. The method of claim 22,wherein the short-distance transmission line emulator comprises aplurality of inductors, the method further comprising: generating, usingthe controller, a short-distance transmission line signal; andprogramming the plurality of switches to couple ones of the plurality ofinductors to each other to adjust a transmission line length of theshort-distance transmission line emulator responsive to theshort-distance transmission line signal.
 24. The method of claim 18,further comprising: generating, using the controller, a mode controlsignal; and configuring each of the plurality of programmable emulatorsas one of a plurality of operating modes responsive to the mode controlsignal.
 25. A computer program product, comprising: a tangible computerreadable storage medium comprising computer readable program codeembodied in the medium that is executable by a processor to performoperations comprising: generating, using a controller, a node controlsignal and a plurality of switch control signals; configuring each of aplurality of programmable emulators as one of a plurality of node typesresponsive to a node control signal from a controller responsive to thenode control signal; and programming a plurality of switches to coupleones of the programmable emulators to each other responsive to theplurality of switch control signals.
 26. The computer program product ofclaim 25, wherein the plurality of programmable emulators comprises afirst plurality of programmable emulators, the operations furthercomprising: configuring each of a second plurality of programmableemulators being configurable as a long-distance transmission lineemulator, a Direct Current (DC) line emulator, a high voltage DCconverter emulator, or a short-distance transmission line emulator;programming the plurality of switches to couple ones of the secondplurality of programmable emulators to each other responsive to theplurality of switch control signals; and programming the plurality ofswitches to couple the ones of the first plurality of programmableemulators to the ones of the second plurality of programmable emulatorsto each other responsive to the plurality of switch control signals.